The surprise decision in Dublin is an early sign of the disruption Brexit may inflict on legal cooperation across the continent. A fresh extradition treaty between the two countries could be needed.

Thomas Joseph O’Connor, 51, a construction company director, from Roscommon, had been convicted of tax fraud in London in 2007 but then absconded on bail and fled to Ireland.

The UK authorities issued a European arrest warrant – the standard procedure that normally guarantees swift delivery within the EU – and O’Connor was arrested by Gardaí.

The Irish supreme court, however, declined to extradite him to the UK and instead ruled that his case should be referred to the European Court of Justice (ECJ) in Luxembourg to resolve the issue.

If returned to the UK, the court noted, he would “continue to be imprisoned in the United Kingdom beyond 29 March, 2019, when the United Kingdom will withdraw from the European Union”.

Lawyers for O’Connor said that Ireland was being asked to surrender an EU citizen to a country where the EU charter of fundamental rights might no longer be capable of enforcement.

“That the debate on potential consequences is not entirely theoretical can be seen from the question which was raised concerning the entitlement of Mr O’Connor to the benefit of a period spent in custody on foot of an earlier European arrest warrant which was found to be invalid,” the five-judge court ruled.

The supreme court concluded that the issue should be passed on to the ECJ – the court whose jurisdiction Brexiters are determined to leave as soon as possible.

“The point is novel and is not the subject of any jurisprudence of the Court of Justice,” the Irish judges said. “However, that is hardly surprising since there has never been a case before of a country leaving the European Union.”